A technique using a heat radiation member over which fins are arranged (heat sink) is known as one of techniques for cooling a semiconductor element which generates heat at the time of operation. The semiconductor element is thermally connected to such a heat radiation member to form a semiconductor module. Traditionally, a metal material, such as copper or aluminum, which has good thermal conductivity has widely been used for making a heat radiation member.
With a heat radiation member made mainly of copper, high heat radiation efficiency is obtained. However, the entire weight is heavy and the cost is high. Accordingly, a composite heat radiation member formed by integrating a member of copper with a member of aluminum which has the advantage in cost or fabrication is also proposed.